(Adds background, details about accidents, paragraphs 2-4)
WASHINGTON, Feb 25 (Reuters) - Shippers moving crude oil by rail out of North Dakota's Bakken energy patch must test the fuel for dangerous volatility before loading it onto the tracks, the U.S. Department of Transportation said on Tuesday.
Last month, officials warned that fuel produced out of the Bakken could be more flammable and explosion-prone than previously thought after a number of explosive derailments over the past year.
"If you intend to move crude oil by rail, then you must test and classify the material appropriately," Department of Transportation Secretary Anthony Foxx said in a statement.
Tuesday's order, which follows other moves to improve safe handling over the past few months, also requires fuel classed 'crude oil' be carried in a "more robust tank car," officials said.
But hazardous material rules still permit any crude oil to be carried on DOT-111 tank cars - the workhorse of oil-by-rail shipments out of North Dakota that regulators say are prone to punture during accidents.
Officials have acknowledged that improvements are needed to the national tank car fleet and they are considering new safety standards.
On Wednesday, DOT officials will join oil and rail executives at a Congressional hearing to discuss safe shipments.
While shippers have always been required to attest to their cargo, industry officials have said testing of Bakken crude has been lax.
In June, an executive with Canadian refiner Irving Oil told an industry conference that sampling protocols for oil-by-rail deliveries were weak. (For full report, please click: r.reuters.com/vun27v)
In July, a crude oil delivery bound for the Irving refinery derailed in the town of Lac Megantic, killing 47. That mishap and two more fiery derailments of oil-by-rail from the Bakken sparked more regulatory scrutiny. (Reporting by Patrick Rucker and Ayesha Rascoe; Editing by Peter Cooney and David Gregorio)